RU2314867C2 - Catalyst for oxidization of the vanadium oxide particles in the gaseous phase with the certain size distribution - Google Patents

Abstract

FIELD: chemical industry; non-ferrous metallurgy industry; other industries; methods of production of the catalyst for oxidization of the vanadium oxide particles in the gaseous phase with the definite size distribution.

SUBSTANCE: the invention is pertaining to the method of production of the catalyst for oxidization in the gaseous phase of the vanadium oxide particles with the definite size distribution. The invention describes the method of production of the catalyst for oxidization in the gaseous phase, at which on the fluidized inert carrier they deposit the suspension of TiO₂ and V₂O₅ particles, in which, at least, 90 volumetric % of the particles of V₂O₅ have the diameter of 20 microns or less and, at least, 95 volumetric % of the particles of V₂O₅ have the diameter of 30 microns or less. The technical result of the invention is that the certain particle-size distribution allows to achieve the high efficiency of the coating.

EFFECT: the invention allows to achieve the high efficiency of the coating.

6 cl, 2 ex

Description

The invention relates to a catalyst for oxidation in the gas phase with a defined particle size distribution of vanadium oxide comprising particles of titanium dioxide and vanadium oxide, to a method for its preparation, as well as to the use of a catalyst for producing phthalic anhydride from o-xylene, naphthalene or mixtures thereof.

Many carboxylic acids and / or carboxylic acid anhydrides are obtained by technically catalytic gas phase oxidation of aromatic hydrocarbons, such as benzene, xylenes, naphthalene, toluene or durene, in fixed bed reactors. In this way, for example, benzoic acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid or pyromelitic anhydride can be obtained. In general, a mixture of oxygen-containing gas and the starting material to be oxidized is passed through pipes in which at least one catalyst is charged. To control the temperature, the pipes are surrounded by a heat-carrying medium, for example, molten salt.

Suitable catalysts for such oxidation reactions are so-called shell catalysts, in which the catalytically active mass is deposited in the form of a shell on an inert carrier, such as steatite. As a catalytically active component of the catalytically active mass of these shell catalysts, vanadium pentoxide generally serves along with titanium dioxide. Further, in a catalytically active mass, many other oxide compounds can be contained in small quantities, which act as promoters on the activity and selectivity of the catalyst.

To obtain such shell catalysts, an aqueous suspension, components of the active mass and / or their precursor compounds are sprayed onto the carrier material at high temperature until the desired fraction of the active mass in the total weight of the catalyst is achieved.

DE-A 2550686 describes a method in which an aqueous solution containing titanium tetrachloride and a vanadium (IV) salt is applied to a carrier.

In the production method described in DE-A 1442590, finely dispersed titanium dioxide in anatase modification is supplied to a solution of vanadyl oxalate, formamide and water. The resulting suspension is applied to an inert catalyst carrier.

Document WO 00/12214 describes a preparation process in which a mixture of titanium dioxide, vanadyl oxalate, an organic binder and, if necessary, promoters is applied by spraying in a coating drum, applying a layer in a fluidized bed or powder coating in the form of a shell in two concentric layers on an inert layer carrier.

EP-A 539878 proposes the preparation of phthalic anhydride catalysts in the gas phase. Ammonium metavanadate is dissolved in an oxalic acid solution and mixed together with the promoters. Then carry out the addition of TiO ₂ , which is obtained from titanium sulfate by sulfate cooking. The resulting suspension is homogenized and sprayed onto a catalyst support at high temperature.

According to DE-A 2106796 and DE-A 19633757, a suspension of anatase and titanium oxide hydrate, V ₂ O ₅ and an organic binder component is applied to the carriers.

Known methods for producing relatively used sources of vanadium can be divided into two classes: in the first case, a soluble compound of vanadium (IV), such as vanadyl oxalate, is used as a source of vanadium. Recovery to vanadium (IV) occurs with an organic reducing agent, for example, oxalic acid. In another case, an insoluble vanadium compound (V), for example V ₂ O ₅ , is added to the aqueous suspension, since there is no requirement for a reducing agent, the cost of the starting materials is small. However, the disadvantage is that the particles of V ₂ O ₅ during the coating process in the fluidized bed are prone to demulsification and do not completely fall onto the substrate to be coated, and are partially released, for example, from process air or deposited on the coating apparatus as a layer. To compensate for the losses, an excess of V ₂ O ₅ should be used. It is advisable to keep this excess as low as possible.

The basis of the invention is the task of developing an economical method for producing gas phase oxidation catalysts containing titanium dioxide and vanadium oxide and the resulting catalyst method.

According to the invention, it was found that the effectiveness of the coating is highly dependent on the particle size distribution of V ₂ O ₅ suspended in the coating suspension.

The invention relates to a catalyst for oxidation in the gas phase, which includes an inert carrier and a catalytically active mass deposited on it, which contains from 1 to 40 wt.% Vanadium oxide, calculated as V ₂ O ₅ , and from 60 to 99 wt.% Dioxide titanium, calculated as TiO ₂ , and obtained by applying a suspension of particles of TiO ₂ and V ₂ O ₅ on the carrier, and in a suspension of at least 90 vol.% particles of V ₂ O ₅ has a diameter of 20 μm or less and at least , 95 vol.% Of particles of V ₂ O ₅ has a diameter of 30 μm or less.

In addition, the invention relates to a method for producing a catalyst for gas phase oxidation, in which a suspension of V ₂ O ₅ and V ₂ O ₅ particles is applied to a fluidized inert carrier, in which at least 90 vol.% V ₂ O ₅ particles has a diameter of 20 microns or less and at least 95 vol.% particles of V ₂ O ₅ has a diameter of 30 microns or less.

Preferably, at least 90 vol.% Of the particles of V ₂ O ₅ has a diameter of 15 microns or less, and at least 95 vol.% Of the particles of V ₂ O ₅ has a diameter of 20 microns or less.

According to a particular embodiment, at least 60 vol.% Of the particles of V ₂ O ₅ has a diameter of 4 microns or at least 80 vol.% Of the particles of V ₂ O ₅ has a diameter of 10 microns or less, at least 90 vol. % V ₂ O ₅ particles have a diameter of 15 μm or less and at least 95% V ₂ O ₅ particles have a diameter of 20 μm or less.

Preferably, at least 50 vol.% Of the particles of V ₂ O ₅ has a diameter of more than 2 microns. The volume calculated D ₅₀ value is preferably from 2.0 to 2.5 μm.

The volume-distributed particle size distribution is determined in an appropriate manner for the purposes of the invention by laser diffraction and Fraunhofer estimation. With this method, parallel-directed laser light is subjected to particle diffraction. Each particle produces a diffraction pattern characteristic of its size. The diffraction spectrum is recorded by the detectors and the particle size distribution as the volume distribution is calculated by the microcomputer.

A particle size distribution suitable for vanadium dioxide can be obtained by sufficiently long milling in suitable mills. For example, reflective mills, roller mills, vibratory mills, mills with grinding bodies (millstones) or inclined mills are suitable. Mills with grinding bodies are preferred. They consist of a horizontally located cylindrical working chamber rotating around a rigid point of rotation. The working chamber is filled with grinding bodies, as a rule, of various sizes. The grinding material is in the volume of voids from the grinding bodies. As grinding bodies, wear-resistant or cast steel balls, rods, respectively, rod segments, are used for wear. Depending on the number of revolutions of the mill, various forms of movement of the grinding bodies are established and this means different types of load of the grinding material, such as friction, stress, breaking and pressure, as a result of which larger particles of the grinding material are crushed.

Preferably, the catalytically active mass contains in a calcined state, calculated on the total amount of the catalytically active mass, from 1 to 40 wt.% Vanadium oxide, calculated as V ₂ O ₅ , and from 60 to 99 wt.% Titanium dioxide, calculated as TiO ₂ , along with this catalytically active mass, may contain up to 1 wt.% Of cesium compound, calculated as Cs, up to 1 wt.% Of phosphorus compound, calculated as P, and up to 10 wt.% Antimony oxide, calculated as Sb ₂ O ₃ .

Along with the optional additives of cesium and phosphorus in the catalytically active mass, in principle, many other oxide compounds can be contained in small quantities, which act as promoters on the activity and selectivity of the catalyst, for example, they increase or decrease its activity. Such promoters include, for example, alkali metal oxides, in particular, in addition to the cesium oxide, lithium, potassium and rubidium oxide, thallium (I) oxide, aluminum oxide, zirconium oxide, iron oxide, nickel oxide, cobalt oxide, oxide manganese, tin oxide, silver oxide, copper oxide, chromium oxide, molybdenum oxide, tungsten oxide, iridium oxide, tantalum oxide, niobium oxide, arsenic oxide, antimony oxide, cerium oxide. As a rule, cesium is used as a promoter from this group.

Further, from the promoters listed, niobium and tungsten oxides are preferred as additives in amounts from 0.01 to 0.50 wt.%, Calculated on the catalytically active mass. Oxidic phosphorus compounds, in particular phosphorus pentoxide, are particularly suitable as enhancing activity, but reducing selectivity of additives.

The titanium dioxide used preferably consists of a mixture of TiO ₂ with a BET surface of 5 to 15 m ² / g and TiO ₂ with a BET surface of 5 to 15 m ² / g. It is also possible to use a single titanium dioxide with a BET surface of 5 to 50 m ² / g, preferably 13 to 28 m ² / g.

As an inert carrier material, practically all carrier materials known from the prior art can be used to obtain shell catalysts for the oxidation of aromatic hydrocarbons to aldehydes, carboxylic acids and / or carboxylic anhydrides, for example quartz (SiO ₂ ), porcelain, magnesium oxide, dioxide tin, silicon carbide, rutile, clay (Al ₂ O ₃ ), aluminum silicate, steatite (magnesium silicate), zirconium silicate, cerium silicate, or mixtures of these materials. Typically, the carrier material is non-porous. The expression "non-porous" in this case should be understood as "up to a technically ineffective number of pores non-porous", since a technically small number of pores in the support material may be present, ideally the material does not contain pores. As preferred carrier materials, steatite and silicon carbide should be highlighted. The shape of the support material is generally not important for the precursor catalyst according to the invention and for the shell catalyst. For example, the catalyst supports may be in the form of balls, rings, tablets, spirals, tubes, extrudates, or crushed stone. The dimensions of these catalyst supports correspond to those commonly used to prepare shell catalysts for partial oxidation of aromatic hydrocarbons in the gas phase. Preferably, steatite is used in the form of balls with a diameter of 3 to 6 or rings with an outer diameter of 5 to 9 mm and a length of 3 to 8 mm and a wall thickness of 1 to 2 mm.

In the method according to the invention, the deposition of the shell catalyst layer (s) is carried out by spraying a suspension of TiO ₂ and V ₂ O ₅ , which, if necessary, contains sources of the aforementioned promoter elements onto a fluidized carrier. Before coating, the suspension is sufficiently mixed for a long time, for example from 2 to 30 hours, in particular from 12 to 25 hours, in order to crush the agglomerates of the suspended solid and obtain a homogeneous suspension. The suspension typically has a solids content of from 20 to 50 wt.%. The suspension medium is generally of an aqueous nature, for example water itself or an aqueous mixture with a water-miscible organic solvent such as methanol, ethanol, isopropanol, formamide and the like.

Typically, organic binders are added to the suspensions, preferably copolymers, preferably in the form of an aqueous dispersion, vinyl acetate and vinyl laurate, vinyl acetate and acrylate, styrene and acrylate, as well as vinyl acetate and ethylene. Binders are commercially available as aqueous dispersions and have a solids content of, for example, 35 to 65% by weight. The amount of such binder dispersions used is generally from 2 to 45% by weight, preferably from 5 to 35% by weight, particularly preferably from 7 to 20% by weight, based on the weight of the suspension.

The carrier is subjected to fluidization in a device with a fluidized bed, respectively, with a fluidized bed in an upward gas stream, in particular air. Devices consist, in most cases, of a conical or spherical vessel in which fluidizing gas is introduced from the bottom up through the immersion pipe. The suspension is injected through nozzles from above, from the side or from below into the fluidized bed. It is preferable to use an ascending pipe located in the middle, respectively, of a concentric located around the immersion pipe. Inside the ascending pipe there is an increased speed that particles transport up. In the outer ring, the gas velocity is only slightly higher than the loosening rate. Thus, the particles move vertically in an annular fashion. A suitable fluidized bed device is described, for example, in DE-A 4006935.

When coating a catalyst support with a catalytically active mass, a temperature of from 20 to 500 ° C. is generally used, and coating can be carried out at atmospheric pressure or under reduced pressure. In general, the coating is carried out at 0 ° C to 200 ° C, preferably at 20 to 150 ° C, in particular from 60 to 120 ° C.

The catalytically active mass can be applied in two or more layers, the inner layer or inner layers can have an antimony oxide content of up to 15 wt.% And the outer layer can have an antimony oxide content reduced by 50 to 100%. However, as a rule, the inner catalyst layer contains phosphorus and the outer layer is poor in phosphorus or does not contain phosphorus.

The thickness of the catalytically active mass layer is typically from 0.02 to 0.2 mm, preferably from 0.05 to 0.15 mm. The proportion of active mass in the catalyst is usually from 5 to 25 wt.%, In most cases from 7 to 15 wt.%.

By heat treatment of the precursor catalyst thus obtained at temperatures from more than 200 to 500 ° C., the binder is volatilized from the deposited layer by thermal decomposition and / or combustion. Preferably, the heat treatment is carried out in situ in a gas phase oxidation reactor.

The catalysts according to the invention are suitable for the gas-phase oxidation of aromatic hydrocarbons with a carbon number of 6 to 10, such as benzene, xylenes, toluene, naphthalene or durene (1, 2, 4, 5-tetramethylbenzene) into carboxylic acids and / or carboxylic anhydrides, such as maleic anhydride, phthalic anhydride, benzoic acid and / or pyromelitic anhydride.

For this purpose, the catalysts prepared according to the invention are filled into the reaction temperature heated externally, for example by means of salt melt, and reaction gas with a temperature of generally from 300 to 450 ° C., preferably from 320 to 420 ° C. is passed over the thus obtained catalyst layer. and particularly preferably from 340 to 400 ° C. and at an overpressure of generally from 0.1 to 2.5 bar, preferably from 0.3 to 1.5 bar, with a space velocity in general of from 750 to 5000 hours

The reaction gas supplied to the catalyst is produced by generally mixing a molecular oxygen-containing gas, which, in addition to oxygen, may also contain suitable reaction inhibitors and / or diluents, such as steam, carbon dioxide and / or nitrogen, with an aromatic hydrocarbon to be oxidized, the gas containing molecular oxygen generally may contain from 1 to 100 mol.%, preferably from 2 to 50 mol.% and particularly preferably from 10 to 30 mol.%, oxygen, from 0 to 30 mol.%, preferably from 0 to 10 mol.%, hydrogen, as well as from 0 to 50 mol.%, pr preferably from 0 to 1 mol. %, carbon dioxide, nitrogen residue. In order to obtain a reaction gas, a molecular aromatic hydrocarbon is generally supplied from 30 g to 150 g per nm ^{3 of} gas to be oxidized with molecular oxygen.

Especially preferred was such an embodiment in which catalysts are used in the catalyst layer that differ in their catalytic activity and / or chemical composition of their active mass. Preferably, when using two catalyst zones in the first zone, i.e. lying on the inlet side of the reaction gas to the reaction zone, a catalyst is used which, compared to the catalyst which is in the second reaction zone lying on the outlet side of the reaction gas, has slightly lower catalytic activity. In general, the reaction is controlled by setting the temperature so that in the first zone most of the aromatic hydrocarbon contained in the reaction gas is converted at maximum yield. Preferably, three to five layer catalyst systems are used, in particular three and four layer catalyst systems.

The invention is explained in more detail using the following examples.

The particle size distribution is measured using a Frisch Particle Sizer "analysette 22" in the measurement range from 0.3 to 300 μm with a resolution of 62 channels. Sample V ₂ O ₅ for measurement is suspended in water and pumped into the measuring cell. The measurement duration is 2 Scans (scan cycles), the assessment is carried out by the Fraunhofer method.

Example 1

54.227 kg of anatase (BET surface of 9 m ² / g), 126.517 kg of anatase (BET surface of 20 m ² / g), 14.195 kg V ₂ O ₅ , 3.549 kg of Sb ₂ O ₃ , 0.805 kg of cesium carbonate are suspended in 519.035 kg deionized water and stirred to obtain a homogeneous distribution. V ₂ O ₅ has the following volume-calculated particle size distribution: 10% ≤0.58 μm; 20% ≤0.87 μm; 30% ≤1.20 μm; 40% ≤1.61 μm; 50% ≤2.21 microns; 60% ≤3.26 microns; 70% ≤5.52 μm; 80% ≤9.46 microns; 90% ≤14.92 microns; 95% ≤19.51 microns; 99.9% ≤169.33 μm. To the suspension was added 80 kg of an organic binder consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50 wt.% Dispersion. In a fluidized bed coating device, 60 kg of this suspension is sprayed onto 150 kg of steatite rings (magnesium silicate) with dimensions of 7 × 7 × 4 mm (outer diameter × height × inner diameter) and dried. The coating is carried out at a temperature of 80-120 ° C and an amount of air of 6000 m ³ / h.

Analysis of the catalysts calcined at 400 ° C. showed that the proportion of V ₂ O ₅ in the active mass was 6.85 wt.%. The calculated target value of the fraction V ₂ O _{5 of the} calcined active mass is in contrast to 7.12 wt.%. There is a missing amount of 0.27% (absolute). To compensate for the loss of V ₂ O ₅ during coating and to obtain a catalyst with a given amount of V ₂ O _5, it was necessary to increase the amount of V ₂ O ₅ in the suspension by 0.543 kg.

Reference Example 2

Example 1 is repeated, and the applied V ₂ O ₅ has the following volume-calculated particle size distribution: 10% ≤0.62 μm; 20% ≤0.93 microns; 30% ≤1.25 μm; 40% ≤1.63 μm; 50% ≤2.10 μm; 60% ≤2.76 μm; 70% ≤3.84 μm; 80% ≤6.27 μm; 90% ≤24.24 microns; 95% ≤46.58 microns; 99.9% ≤300 μm.

Analysis of the catalysts calcined at 400 ° C. showed that the proportion of V ₂ O ₅ in the active mass was 5.55 wt.%. With respect to a predetermined value of 7.12 wt.%, The missing amount is 1.57% (absolute). To compensate for the loss of V ₂ O ₅ during coating and to obtain a catalyst with a given amount of V ₂ O _5, it was necessary to increase the amount of V ₂ O ₅ in the suspension by 3.134 kg.

The above examples show that the use of V ₂ O ₅ with a specific particle size distribution can reduce its required applied amount.

Claims (6)

1. A method of producing a catalyst for oxidation in the gas phase, in which a suspension of TiO ₂ and V ₂ O ₅ particles is applied to the fluidized inert carrier, in which at least 90 vol.% Of V ₂ O ₅ particles has a diameter of 20 μm or less and at least 95 vol.% of particles of V ₂ O ₅ has a diameter of 30 μm or less. 2. The method according to claim 1, characterized in that at least 90 vol.% Of particles of V ₂ O ₅ has a diameter of 15 μm or less and at least 95 vol.% Of particles of V ₂ O ₅ has a diameter of 20 microns or less. 3. The method according to claim 1 or 2, characterized in that at least 50 vol.% Particles of V ₂ O ₅ has a diameter of more than 2 microns. 4. The method according to claim 1 or 2, characterized in that the suspension, in addition, contains at least one source of cesium, phosphorus and / or antimony. 5. The method according to claim 1 or 2, characterized in that the supported catalytically active mass contains from 1 to 40 wt.% Vanadium oxide, calculated as V ₂ O ₅ , and from 60 to 99 wt.% Titanium dioxide, calculated as TiO ₂ . 6. The method according to claim 5, characterized in that the catalytically active mass contains up to 1 wt.% Cesium compound, calculated as Cs, up to 1 wt.% Phosphorus compound, calculated as P and up to 10 wt.% Antimony oxide, calculated as Sb ₂ O ₃ .